It is known that a Diesel engine is generally equipped with an injection system that includes a plurality of electrically controlled fuel injectors for injecting fuel directly into cylinders. The fuel injection in each cylinder is generally performed according to a multi-injection pattern having a plurality of injection pulses per engine cycle, including at least one pilot injection, i.e. a fuel injection in a cylinder of the engine that occurs before the Top Dead Center (TDC) of the piston, and one main injection, i.e. a fuel injection that occurs near to the TDC.
In order to increase the temperature of the exhaust gas for regenerating aftertreatment devices, such as for example a diesel particulate filter, or for warming-up the aftertreatment devices, it is known from GB2472816 to perform a multi-injection pattern which includes a plurality of so-called after injections, i.e. fuel injections that start after the main injection or after the piston has passed its top dead center (TDC) position, but still sufficiently near to the TDC for the fuel to burn at least partially inside the cylinder. In practice, the plurality of after injections define a so-called multi after-injection pattern within the multi-injection pattern.
However, the fuel quantity injected by the multi after-injection pattern and the timing of the injection pulses of the multi after-injection pattern impacts on the oil dilution and the fuel consumption of the internal combustion engine, so that a need exists of a method that improves the efficiency of the multi after-injection pattern.